Method of cleaning azo printed regenerated cellulose gel with hydrated alumina



Patented Apr. 4, 1950 METHOD OF CLEANING AZO PRINTED RE- GENERATED CELLULOSE GEL WITH HY- DRATED ALUMIN A Edward L. Wolfram, Buffalo, N. Y.

No Drawing. Application August 7, 1947, Serial No. 767,339

4 Claims.

The present invention relates to a method of cleaning printed regenerated cellulose articles in the gel state as, for instance, printed caps, bands, sheets and the like.

In printing the caps and bands of regenerated cellulose so extensively employed a protective covers for numerous articles, it has been found most advantageous to print the pellicular material while wet and, more particularly, whil the same is in the gel state. Thus, the pellicle, as for instance a band, is made by coating a mandrel with a celllllOsic solution such as a viscose solution, for example, by immersing the mandrel into the solution and after withdrawing the coated mandrel, coagulating the viscose adhering thereto. The coagulated material is subsequently subjected to a regenerating bath of conventional type and purified by desulfuring, bleaching and washing in conventional way.

The bleached band of regenerated cellulose is in a rubbery condition where it is relatively porous, that is, in the so-called gel state. The pellicular material in the gel state is then subjected to a print operation which essentially comprises the formation of a colored material on predetermined areas of the regenerated cellulosic article, While it is still in the gel state. This i generally accomplished by treating the article, while in the gel state, successively with two substances which react to form a coloring agent as, for instance, the formation of a coupled dye such as a diazo dye on the area of the article in which it is desired to produce an indicia. Or, an oxidized leuco compound may be produced in a predetermined area of the article where printing matter of any kind is desired.

In general, the article as, for instance, a cap or band of regenerated cellulose, while in the gel state and after any superficial or surface moisture has been removed, is impregnated either com pletely or at predetermined areas with one of such coupling reagents, for example, with either a diazo diazonium compound or a leuco base. Thereafter a complementary coupling reagent, for example, a substance which develops the diazo dye or oxidizes the leuco base is applied at the predetermined areas generally by means of a die or stamp which carries and applies the developer.

Or, as is more preferable, the article of regenerated cellulose in the gel state is impregnated with the developer or oxidizer and the diazo compound or leuco base then applied by means of a die or stamp formed in the outline of the material to be printed upon the article. The print-- ing of regenerated cellulose, and particularly the printing of caps and bands for bottles, is almost uniformly carried out by the latter procedure wherein the gel is impregnated with developer.

The article of regenerated cellulose is therefore uniformly off color by reason of .the presence therein of such developer. Where the developer comprises a material such as naphthol AS, the gel is colored a light yellow and, after printing the cap or band, must be subjected to a lengthy bleachin operation with hypochlorite to elimi nate and destroy the excess of the developer. The article is then treated with an anti-chlor and washed to leave the unprinted background in its original white, bleached condition.

It is an object of the present invention to provide a procedure for eliminating the excess coupling reagent present in the unprinted background portion of regenerated cellulose which has been printed in the gel state by developing a dye therein at predetermined areas.

It is also an object of the invention to eliminate the costly and lengthy hypochlorite treatment heretofore employed to remov excess of dye developer present in the unprinted background of regenerated cellulosic articles that have been printed in the gel state by developing the dye thereon in predetermined areas.

It is also an object of the invention to employ a physical method of eliminating the excess de veloper in the unprinted background of regenerated cellulosic articles that have been printed in the gel state.

In accordanc with the present invention, an article of regenerated cellulosic material that has been printed in the gel state by developing therein a dye on predetermined areas is, while still in the gel state, treated with an aqueous solution of an aluminum salt at a pH insufficient to injure the regenerated cellulosic article but sufficient to produce an incipient precipitate of aluminum hydroxide in the solution and in contact with the gel.

In some instances an aqueous solution of aluminum sulfate may be prepared and treated r with suificient alkali to produce an incipient precipitate of aluminum hydroxide in the solution, and the article of regenerated cellulose in the gel state containing printed matter thereon and containing an unwanted developer in the unprinted background, is immersed in or passed continuously through this solution until the color in the unprinted background has been removed. The article is then removed from the solution of aluminum sulfate, washed and wound on spools in conventional way for shipment and use.

Where the article of regenerated cellulose in the gel stage has been printed under conditions where the gel contains a portion of alkali, the article may be passed directly into a solution of an aluminum salt as, for instance, aluminum sulfate, and an incipient precipitate of aluminum hydroxide is formed directly on the surface, or in contact with the surface, of the article and absorbs or removes the colored matter from the unprinted background of the article.

In general, substantially any concentration of aluminum salt is suitable for this purpose, provided there be suflicient to produce an amount of precipitate capable of removing the unwanted developer or coloring matter in the unprinted background. In practical operation, two parts of water by weight to one part aluminum sulfate by weight is eminently satisfactory, although the proportions may vary greatly from this figure.

The solution may be made with any aluminum salt provided only that an incipient precipitate be formed in the solution by an alkali prior to the treatment of the printed article therewith, or is capable of being formed therein by the alkali present in the regenerated cellulosic gel. In general, the pH of the aluminum solution may vary from about pH 3 to about pH 8 /2, although the pH may vary slightly above or below such limits depending upon the history of the article being treated. Aluminum sulfate, alum, aluminum chloride and substantially any soluble aluminum salt is suitable for the purpose.

Although the mechanism of the successful action of the aluminum salt solution is not definitely known, it is believed that the precipitated hydrated aluminum oxide or hydroxide possesses a greater affinity for the colored developer than does the gel form of regenerated cellulose and thus the developer is transferred from the gel to and absorbed by the hydrated aluminum compound. However, whatever be the mechanism, a simple immersion or washing of the dyed gel is sufiicient to eliminate from the background thereof, the excess of colored developer, and leave such background in its original bleached condition.

The following examples are given as illustrative of the invention and are not to be deemed limitative thereof as there are many variations of dye and developer known in the art, see for instance, Letters Patent of the United States of America, No. 1,997,769, of George A. Fletcher, issued April 16, 1935.

A beverage bottle band of bleached regenerated cellulose in the gel state was impregnated with a developer containing alkaline naphthol AS (anilide of betahydroxynaphthoic acid) and indicia printed thereupon. The unprinted portions were a light lemon color in shade. This color was eliminated by passing the band still in the gel state and containing alkali through an aqueous solution containing 15% by weight of crystallized aluminum sulfate. As the alkali in and upon the band was suflicient to produce a precipitate of aluminum hydroxide upon the surface of the band, no additional alkali was added to the original solution of the aluminum sulfate. The band was immersed for a period of 2 /2 seconds at a temperature of 85 C. Upon discharge from the purifying solution it was passed through wash water and rolled on spools. The transparent undyed background was in the initial bleached condition. The tint of the dye was enhanced in brilliancy probably by reason of a fixative or modant action of the aluminum salt.

Similar excellent results were obtained with naphthol AS-G (diaceto-acet-o-tolidide) and with naphthol AS-BG (2:5 dimethoxy anilide of betahydroxynaphthoic acid).

Although the purifying action of the present invention has been illustrated by operations slightly above room temperature, it will be understood that the operations may also be performed in hot solutions and the washing performed with hot water.

The total operating time necessary for removing the excess developer from the unprinted portions of the article is a matter of seconds and when operated continuously produces excellent results. It will be apparent that the invention contemplates the removal of the developer by bringing the printed article in gel form in contact with a hydrated oxide possessing an afifinity for the developer which is greater than that possessed by the gel, whereby the developer is removed from the gel.

The specific examples have been illustrated by the use of bleached tubing. It will be understood that the same action is obtained when unbleached tubing is printed.

What is claimed is:

l. The method of removing excess of azo dye component from regenerated cellulosic articles that have been printed in the gel state by coupling azo dye-forming components in the printing thereof which comprises depositing a film of hydrated aluminum hydroxide on the article while still in the gel state and subsequently washing the article with water while still in the gel state after such hydroxide has adsorbed undesired residue of dye component to remove said hydroxide and excess reagent from said article.

2. The method of removing excess of azo dye component from regenerated cellulosic articles that have been printed in the gel state by coupling azo dye-forming components in the printing thereof which comprises treating the article while still in the gel state with an aqueous solution of an aluminum salt at a pH within the range of about pH 3 to pH 8.5 in the presence of sufiicient alkali to precipitate aluminum hydroxide in contact with the article and subsequently washing the article with water while still in the gel state after such hydroxide has adsorbed undesired residue of dye component to remove said hydroxide and excess reagent from said article.

3. The method of removing excess of azo dye component from regenerated cellulosic articles that have been printed in the gel state by coupling azo dye-forming components in the printing thereof which comprises passing said article while still in the gel state and containing suflicient alkali to form aluminum hydroxide, through an aqueous solution of an aluminum salt at a pH within the range of about pH 3 to pH 8.5 to precipitate aluminum hydroxide in contact with the article and subsequently washing th article with water while still in the gel state after such hydroxide has adsorbed undesired residue of dye component to remove said hydroxide and excess reagent from said articles.

4. The method of removing excess of azo dye component from regenerated cellulose articles that have been printed in the gel state by coupling azo dye forming components in the printing thereof which comprises passing the printed article in gel form first through an aqueous suspension containing aluminum hydroxide whereby the excess of said azo dye component is transferred from the unprinted portions of said article to 5 said, aluminum hydroxide, thereafter passing said article still in gel form through wash water to remove excess hydroxide frOm said article and thereafter winding the article upon a spool.

EDWARD L. WOLFRAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Re. 19,527 21,786 63,420 1,540,446 1,997,769

Name Date Laska Apr. 9, 1935 Tucker Oct. 12, 1858 Paraf Apr. 2, 1867 Wilson June 2, 1925 Fletcher Apr. 16, 1935 

1. THE METHOD OF REMOVING EXCESS OF AZO DYE COMPONENT FROM REGENERATED CELLULOSIC ARTICLES THAT HAVE BEEN PRINTED IN THE GEL STATE BY COUPLING AZO DYE-FORMING COMPONENTS IN THE PRINTING THEREOF WHICH COMPRISES DEPOSITING A FILM OF HYDRATED ALUMINUM HYDROXIDE ON THE ARTICLE WHILE STILL IN THE GEL STATE AND SUBSEQUENTLY WASHING THE ARTICLE WITH WATER WHILE STILL IN THE GEL STATE AFTER SUCH HYDROXIDE HAS ADSORBED UNDESIRED RESIDUE OF DYE COMPONENT TO REMOVE SAID HYDROXIDE AND EXCESS REAGENT FROM SAID ARTICLE. 